Sr x Ti 0.6 Fe 0.4 O 3− δ ( x = 1.0, 0.9) catalysts for ammonia synthesis via proton-conducting solid oxide electrolysis cells (PCECs)

Ammonia is a promising carbon-free energy carrier. Ammonia is usually industrially synthesized via the Haber–Bosch method under high pressures and temperatures, which requires high energy consumption. In comparison, the electrocatalytic reduction of N 2 is a green, eco-friendly, and pollution-free method for ammonia synthesis if the electricity is generated using a renewable source. Therefore, the development of highly efficient electrocatalysts for the N 2 reduction reaction (NRR) would be significant. Herein, perovskites Sr x Ti 0.6 Fe 0.4 O 3− δ (S x TF, x = 1 and 0.9) with tunable oxygen vacancies (OVs) were prepared and used as NRR electrodes for proton-conducting solid oxide electrolysis cells (PCECs). These PCECs were used to synthesize NH 3 from N 2 and H 2 . STF and S 0.9 TF showed maximum ammonia synthesis rates of 6.84 × 10 −9 (±0.25 × 10 −9 ) mol cm −2 s −1 and 4.09 × 10 −9 (±0.80 × 10 −9 ) mol cm −2 s −1 , with corresponding Faraday efficiencies of 2.79% (±0.12%) and 2.01% (±0.09%) at 650 °C and 0.6 V. The enhanced NRR performance of S 0.9 TF was mainly attributed to the improved adsorption and activation of N 2 by the abundant OVs, Ti 3+ and the exsolved Fe active particles. This work offers a promising strategy for the design of materials for the electrochemical synthesis of NH 3 via PCECs.